1. Field of the Invention
The present invention relates to a gas sensor having a gas sensor element for detecting the concentration of a particular gas.
2. Description of the Related Art
A gas sensor is mounted to an intake system (e.g., an intake pipe or an intake manifold) of an internal combustion engine, such as a diesel engine or a gasoline engine, in order to control, for example, the condition of combustion by monitoring the concentration of a particular gas. Conventionally, such a gas sensor has the following structure: a gas detection element is held in a housing made of metal, and various terminals, a separator, etc., provided at a proximal side (rear side) of the housing are protected with a tubular cover made of metal.
However, the cover made of metal is problematic in that, since the structure is intricate, manufacture or assembly consumes time and labor. In order to cope with this problem, a structure has been developed as described in Patent Document 1 in which a base member made of resin is connected to a proximal end portion of the housing.
Meanwhile, in order to mitigate the impact imposed on a colliding object with which a vehicle having an internal combustion engine collides, a clearance must be provided between the hood and engine parts. In this connection, the length of outward projection of the gas sensor from the intake pipe must be shortened.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. H10-132779
3. Problems to be Solved by the Invention
However, in the gas sensor having a base member made of resin, in order to shorten the length of outward projection of the gas sensor from the intake pipe with the length (size) of the gas detection element being held unchanged, the gas sensor must be inserted deeper into the intake pipe. As a result, the connection between the base member and the housing is positioned within a sensor mounting hole of the intake pipe.
Meanwhile, according to the gas sensor of Patent Document 1, the heat of a heater for heating the gas detection element, the heat of intake gas, etc., are transmitted directly to the intake pipe from the housing, thereby reducing thermal influence on the base member. However, a problem arises with the above-mentioned configuration: since the heat is partially transmitted to the intake pipe from the housing via the above-mentioned connection, a large thermal load (e.g., 200° C. or higher) is imposed on a front end portion of the base member made of resin.